Method of coating magnesium and magnesium alloy articles

ABSTRACT

A method of coating a fine particulate material on magnesium or magnesium alloy articles employing discrete carrier particles to apply a filming liquid and the fine particulate coating material to the article surface in separate steps.

United States Patent [72] Inventor Henry A. Kuchek Auburn, Mich.

[21] Appl. No. 733,810

[22] Filed June 3, 1968 [45] Patented Nov. 2, 1971 [73] Assignee The Dow Chemical Company Midland, Mich.

[54] METHOD OF COATING MAGNESIUM AND MAGNESIUM ALLOY ARTICLES 6 Claims, No Drawings [52] U.S.Cl ll7/7lM, 117/109,ll7/l3l,106/1,29/191.2 [51] lnt.Cl B44c3/02,

[50] Field of Search 117/109, 119.6,131, 71; 106/], 286; 29/1912, 31

[56] References Cited UNITED STATES PATENTS 3,395,027 7/1968 Klotz 117/131 X Primary Examiner-Alfred L. Leavitt Assistant Examiner- Edward G. Whitby An0meysGriswold and Burdick, C. Kenneth Bjork and Lloyd S. .Iowanovitz ABSTRACT: A method of coating a fine particulate material on magnesium or magnesium alloy articles employing discrete carrier particles to apply a filming liquid and the fine particulate coating material to the article surface in separate steps.

METHOD OF COATING MAGNEIUM AND MAGNESIUM ALLOY ARTICLES BACKGROUND OF THE INVENTION In metallurgical processes it is ofien desired to apply a coating of fine particulate material to articles formed of a metal, a metalloid or an alloy in order to produce compositions not readily obtainable in a more conventional manner. For example, alloying ingredients which form an insoluble phase in molten basis metal at casting temperature may nonetheless be in corporated into the alloy in proper amount. A small percent of alloying ingredient in finely divided form is dispersed throughout the article which may then be further worked if necessary to provide a useful article of manufacture. A problem arising in such operations is the obtaining of substantially uniform dispersion of the fine particulate material as well as adequate adherence of the fine particulate material to the alloy article.

The term magnesium" as used herein refers to magnesium and any alloy of magnesium containing at least 50 weight percent magnesium.

lt is therefore a principal object of the invention to provide a method of coating magnesium articles with a fine particulate material.

A further object is to obtain improved adherence of fine particulate material to such articles.

These and other objects and advantages of the present invention will be made apparent to those skilled in the art upon becoming familiar with the following description.

THE INVENTION The method of the present invention comprises l contacting at least one magnesium article to be coated with discrete carrier particles and a filming liquid, thereby wetting the surface of the article with filming liquid; (2) contacting the sowetted article with discrete carrier particles, a fine particulate coating material, and a filming liquid, thereby imparting to the article a layer of particulate coating material. Ordinarily, in commercial operations a plurality of magnesium articles are treated at one time.

Proportions of the materials which can be used, based on the weight of carrier particles, are as follows: 95 to 1000 parts of discrete carrier particles, 0.2 to 1.0 weight percent filming liquid, and l part by weight particulate coating material.

The discrete carrier particles used may be metals, metalloids or alloys, e.g., those normally made by jet or wheel atomizing a molten material. Examples of such particle materials are magnesium, aluminum, iron, silver, lead, copper, zinc, silicon, tellurium, boron, and sand. Sizes of the discrete particles are mainly in the range of to 120 mesh (U.S. Sieve Series), though some particles may run to a size of 4 mesh or coarser, and some finer than l20 mesh may be used.

The fine particulate coating material is employed as a finely divided powder and consists of most any material that is desired to be coated on the article, e.g., either metal or nonmetals. Examples of such materials to be applied are aluminum, copper, silver, gold, beryllium, tin, tungsten, aluminum oxide, boron nitride, tungsten carbide, and the like.

The more useful coating materials are employed in particulate form having a longest average particle dimension not over about one-tenth that of the discrete carrier particles material. While the fine particulate material may be equiaxed, it is preferable that it is employed in the form of flakes.

The filming liquid used is most any material which is liquid at the temperature at which the particulate coating material and carrier particles are to be blended. Generally suitable are liquids boiling in the range of about 40 to 350 C., having a capability of wetting the fine particulate coating material, the carrier particles and the article to be coated, having a surface tension greater than about 20 dynes per centimeter, and more preferably greater than about 30 dynes per centimeter, and being substantially unreactive towards the fine particulate coating material, the carrier particles and the article to be coated.

Examples of suitable filming liquids are: ethylene glycol, glycerol, carbon tetrachloride, water, hydrazine hydrate, ethyl carbonate, ethyl oxalate, methyl oxazolidinone, and mixtures thereof, and binary mixtures of ethylene glycol and ethyl alcohol.

ln carrying out the coating process, the article to be coated is contacted with discrete carrier particles and filming liquid, as by tumbling in a rotating cylinder, e.g., a ball mill jar having the balls removed to coat the article with filming liquid. Contact time varies with quantity, but generally is completed in 2 to 8 hours or more. Some materials blend thoroughly in about 3 minutes using a shaking type mixer such as a commercial apparatus used for mixing paint in the can in paint stores. Preferably, the carrier particles and the filming liquid are admixed prior to contacting with the article. The article may be any size and shape, simple or complex.

The so-wetted article is contacted with, in addition to the carrier particles and filming liquid, a fine particulate coating material. More preferably, discrete carrier particles are first blended and thoroughly wetted with the filming liquid, and then the fine particulate coating materials added and blended before the article to be coated is placed in contact therewith.

The coating process of the present invention has the advantage of being able to coat articles of unusual shapes, e.g., articles having recessed areas. The carrier particles "share" the filming agent of the first mixture and the coating material of the second mixture, thereby uniformly covering the article with a layer of coating material. The article may then be heat treated to diffuse the coating material into the article or otherwise further processed to produce a useful article of manufacture.

if desired, articles may also be coated with successive layers of differing fine particulate materials, respectively. Thus afler application of a first layer, the second material is added without heating such initially coated articles. In this manner, articles of magnesium-base alloy can be coated with tungsten carbide powder and then with aluminum powder using the present method.

The process of the present invention is such that a multiplicity of magnesium articles of varying sizes and shapes may be coated together in a batch or continuous manner.

The following examples are to be considered as illustrative only and not as limiting the scope of the invention.

EXAMPLE I About 6 ml. of ethylene glycol were added to 1,000 grams of atomized magnesium base alloy pellets containing about 1 percent Zn and about 0.6 percent Zr, and a magnesium alloy article having dimensions of about 1%)(395X3/l0 inches to be coated in a container and the container shaken for about 3 minutes. The article had a nominal composition of about 3 weight percent aluminum, about l weight percent zinc, about 0.2 weight percent manganese, balance magnesium. About 20 grams of paint grade aluminum powder were added and the container shaken for another 3 minutes. The article was removed and dried for 16 hours at about 650 F.

The article was unifonnly coated with a thin, smooth layer of aluminum indicating excellent close adherence of the aluminum powder to the article.

EXAMPLE I! About 6 ml. of ethylene glycol were blended with 1,000 grams of atomized magnesium base alloy pellets described above (20 to mesh size, U.S. Standard Sieve Series) to form a first mixture. About 6 ml. of ethylene glycol were preblended with 1,000 grams of the atomized magnesium base alloy pellets and the resulting mix blended with about 25 grams of paint grade aluminum powder to form a second mixture. A magnesium base alloy article of the same composition and size as described for the preceding run was placed in a container holding the first mixture and the container shaken for 3 minutes. The article was removed and placed in a second container holding the second mixture. The second container was shaken for about 3 minutes. The article was removed and dried for 16 hours at 650 F.

The article was unifonnly coated with a thin, smooth layer of aluminum indicating excellent close adherence of the aluminum powder to the article.

It is understood that the above examples of coating one article of a particular magnesium alloy are representative only. In a similar manner a plurality of magnesium articles can be coated with a particular material by the two-stage contacting process, e.g. using a barrel mixer, of the present invention.

The method of the invention having been thus described, various modifications thereof will at once be apparent to those skilled in the art and the scope of the invention is to be considered limited only by the claims hereafter appended.

What is claimed is:

l. A method of coating at least one magnesium article with a fine particulate material which comprises:

a. contacting a magnesium article to be coated with discrete carrier particles and a filming liquid, thereby wetting the surface of said article with said filming liquid;

b. contacting the so-wetted article with discrete carrier particles, a filming liquid and a fine particulate coating material which has a longest average particle dimension not over about one-tenth that of the discrete carrier particles, thereby coating the article with said particulate coating material; and

c. drying the article.

2. The method of claim 1 wherein in step (a) the carrier particles are first mixed with said filming liquid and the resulting mixture is contacted with the magnesium article; and wherein in step (b) the carrier particles are first mixed with said filming liquid and said particulate coating material and thereafter the mixture is contacted with the article.

3. The method of claim 1 wherein after step (b) the coated article is contacted with discrete carrier particles, a filming liquid and a second fine particulate material which has a longest average particle dimension not over about one-tenth that of the discrete carrier particles.

4. The method as in claim 1 wherein the fine particulate material is aluminum.

5. The method as in claim 1 wherein the filming liquid is a member selected from the group consisting of carbon tetrachloride, glycerol, ethylene glycol, ethyl alcohol. a binary mixture of ethylene glycol and ethyl alcohol, water. ethyl carbonate, ethyl oxalate, hydrazine hydrate and methyl oxazolidinone and mixtures thereof.

6. The method as in claim 1 in which the filming liquid is ethylene glycol. 

2. The method of claim 1 wherein in step (a) the carrier particles are first mixed with said filming liquid and the resulting mixture is contacted with the magnesium article; and wherein in step (b) the carrier particles are first mixed with said filming liquid and said particulate coating material and thereafter the mixture is contacted with the article.
 3. The method of claim 1 wherein after step (b) the coated article is contacted with discrete carrier particles, a filming liquid and a second fine particulate material which has a longest average particle dimension not over about one-tenth that of the discrete carrier particles.
 4. The method as in claim 1 wherein the fine particulate material is aluminum.
 5. The method as in claim 1 wherein the filming liquid is a member selected from the group consisting of carbon tetrachloride, glycerol, ethylene glycol, ethyl alcohol, a binary mixture of ethylene glycol and ethyl alcohol, water, ethyl carbonate, ethyl oxalate, hydrazine hydrate and methyl oxazolidinone and mixtures thereof.
 6. The method as in claim 1 in which the filming liquid is ethylene glycol. 